1. Field of the Invention
The present invention relates to a bubble jet type ink-jet printhead. More particularly, the present invention relates to a high-density ink-jet printhead in which a plurality of nozzles, through which ink is ejected, are arrayed on an ink supply manifold in a plurality of rows, thereby increasing the number of nozzles per unit area.
2. Description of the Related Art
In general, ink-jet printheads are apparatuses that eject a fine droplet of printer ink on a desired position of a paper to print an image containing one or more predetermined colors. To eject ink onto the paper, an ink-jet printer generally adopts an electro-thermal transducer method that ejects ink onto the paper by generating a bubble in ink using a heat source (this method is called a bubble jet type), or an electromechanical transducer method that ejects ink onto the paper using a change in the volume of ink due to the deformation of a piezoelectric body.
In a bubble-jet type ink ejection mechanism, as mentioned above, when power is applied to a heater including a resistance heating element, ink adjacent to the heater is rapidly heated to about 300xc2x0 C. Heating the ink generates bubbles, which grow and swell, and thus apply pressure in the ink chamber filled with the ink. As a result, ink adjacent to a nozzle is ejected from the ink chamber through the nozzle.
There are multiple factors and parameters to consider in making an ink-jet printhead having an ink ejecting unit in a bubble-jet mode. First, it should be simple to manufacture, have a low manufacturing cost, and be capable of being mass-produced. Second, in order to produce high quality color images, the formation of undesirable satellite ink droplets that usually accompany an ejected main ink droplet must be avoided during the printing process. Third, cross-talk between adjacent nozzles, from which ink is not ejected, must be avoided, when ink is ejected from one nozzle, or when an ink chamber is refilled with ink after ink is ejected. For this purpose, ink back flow, i.e., when ink flows in a direction opposite to the direction in which ink is ejected, should be prevented. Fourth, for high-speed printing, the refilling period after ink is ejected should be as short a period of time as possible to increase the printing speed. That is, the driving frequency of the printhead should be high.
The above requirements, however, tend to conflict with one another. Furthermore, the performance of an ink-jet printhead is closely related to and affected by the structure and design, e.g., the relative sizes of ink chamber, ink passage, and heater, etc., as well as by the formation and expansion shape of the bubbles.
FIG. 1A illustrates an exploded perspective view of a structure of an ink ejector of a conventional bubble jet type ink-jet printhead according to the prior art. FIG. 1B illustrates a cross-sectional view for explaining a process of ejecting an ink droplet from a conventional bubble jet type ink-jet printhead. FIG. 1C illustrates a plan view of the arrangement of a plurality of nozzles in the conventional inkjet printhead of FIG. 1A.
A conventional bubble jet type ink-jet printhead shown in FIGS. 1A through 1C includes a substrate 10, barrier walls 38 that are formed on the substrate 10 and that form ink chambers 26, which are filled with ink 49, heaters 12 formed in the ink chambers 26, and a nozzle plate 18 having nozzles 16 from which an ink droplet 49xe2x80x2 is ejected. The ink 49 is supplied to the ink chambers 26 via ink channels 24 from ink supply manifolds 14 in flow communication with an ink storage unit (not shown). As a result, the nozzles 16, which are in flow communication with the ink chambers 26, are also filled with the ink 49 due to capillary action. In the above ink-jet printhead, a plurality of heaters 12 and a plurality of ink chambers 26 are formed to correspond to the plurality of nozzles 16, and are arranged in a row, adjacent to each of the ink supply manifolds 14.
In operation of the above ink-jet printhead, the heaters 12 are supplied with current and heated to form bubbles 48 in the ink 49 filled in the ink chambers 26. Then, the bubbles 48 expand and put pressure on the ink 49 filled in the ink chambers 26, thereby ejecting an ink droplet 49xe2x80x2 to the outside via the nozzles 16. Then, the ink 49 flows through the ink channels 24 to fill the ink chambers 26.
A process of manufacturing a conventional printhead having the above structure, however, is complicated because the nozzle plate 18 and the substrate 10 are individually made and then bonded together. In particular, the nozzle plate 18 may be misaligned with respect to the substrate 10 during manufacture.
Additionally, as previously mentioned, the plurality of nozzles 16, heaters 12 and ink chambers 26 are arranged on each manifold 14 in a row, but may be arranged at both sides of each manifold 14 in a row. With such a structure, however, there is a limitation in increasing the number of nozzles per unit area, i.e., the density of a nozzle. Accordingly, it is difficult to realize a high-density ink-jet printhead that prints quickly and has high resolution.
In an effort to solve the above problems, it is a feature of an embodiment of the present invention to provide a high-density ink-jet printhead in which hemispherical ink chambers are formed that satisfy the above conditions, and a plurality of nozzles are arranged on each ink supply manifold in a plurality of rows, thereby increasing the density of nozzles.
To provide the above feature, there is provided an ink-jet printhead including a substrate; a plurality of ink chambers formed in a hemispherical shape at a surface of the substrate and filled with ink; a manifold formed at a rear surface of the substrate, the manifold for supplying ink to the plurality of ink chambers; a plurality of ink channels each formed at a bottom of each of the plurality of ink chambers to be in flow communication with the manifold; a nozzle plate monolithically formed with the substrate; a plurality of nozzles formed on the nozzle plate, each formed to correspond to a center of each of the plurality of ink chambers; a plurality of heaters formed on the nozzle plate, each of the plurality of heaters having a ring shape and encircling a corresponding one of the plurality of nozzles; and a plurality of electrodes positioned on the nozzle plate and electrically connected to the plurality of heaters, the plurality of electrodes applying current to the heaters.
In an embodiment of the present invention, the plurality of nozzles are arrayed on the manifold in at least three rows. In a preferred embodiment of the present invention, the plurality of nozzles are arrayed on the manifold in five rows.
Preferably, the substrate is a silicon wafer and the nozzle plate is a silicon oxide layer formed by oxidizing a surface of the silicon wafer.
Preferably, each of the plurality of nozzles may have a nozzle guide extending in the depth direction of the ink chamber, at each edge of the plurality of nozzles.